Centrifuge rotor

ABSTRACT

A rotor for a centrifuge apparatus having a substantially cylindrical sidewall forming a bowl-like chamber open on one side thereof, and including a cover secured to the cylindrical sidewall and closing the opening to the chamber. The rotor also includes a resilient sealing lip attached to the sidewall and overhanging the chamber, the lip having an upper surface engaging a lower surface of the cover and having sufficient resiliency to follow movement of the cover under hydrostatic pressures produced in the rotor during centrifugation of liquid products within the chamber.

States atent [19] Schmidt et a1.

CENTRIFUGE ROTGR Inventors: William L. Schmidt, Boulder, Colo.;

Herschel E. Wright, Santa Clara, Calif.

Beckman Instruments, lnc., Fullerton, Calif.

Filed: Apr. 116, 1973 Appl. No.: 351,364

Assignee:

US. Cl. 233/27, 233/32 Int. Cl B0411) 7/06 Field of Search 233/1 R, 26,32, 33, 44, 233/27, 28, 46, 1 B, 1 A

References Cited UNITED STATES PATENTS.

4/1893 Hart 233/44 2/1965 Stallman et a1. 233/33 3/1969 Gibson et a]233/33 X [451 Oct. 22, 1974 3,536,253 10/1970 Anderson ..233/333,675,846 7/1972 Drucker ..233/26 Primary Examiner-George l-l.Krizmanich Attorney, Agent, or Firm-R. J. Steinmeyer; F. L. Mehlhoff 57ABSTRACT A rotor for a centrifuge apparatus having a substantiallycylindrical sidewall forming a bowl-like chamber open on one sidethereof, and including a cover secured to the cylindrical sidewall andclosing the opening to the chamber. The rotor also includes a resilientsealing lip attached to the sidewall and overhanging the chamber, thelip having an upper surface engaging a lower. surface of the cover andhaving sufficient resiliency to follow movement of the cover underhydrostatic pressures produced in the rotor during centrifugation ofliquid products within the chamber.

5 Claims, 2 Drawing Figures csnrnrrucs noron BACKGROUND OF THE INVENTIONThe invention described herein relates generally to rotors forcentrifuge apparatus and more particularly to an improved bowl-typerotor of the type employed for zonal centrifugation.

The apparatus is utilized to provide quantitative separations of minuteparticulate matter, such as tissue cells or cell particles, or the like,in density gradients for the purpose of collecting discrete fractionsthereof for subsequent analysis in research and clinical studies.Typically, in a bowl-type rotor, a sample solution is pumped into thecentral region of a rotor chamber which is filled with an appropriatedensity gradient solution. During centrifugation, the particles ofinterest in the sample disperse in a radial direction throughout thedensity gradient solution and at equilibrium are suspended in concentriclayers in the density gradient solution at a location wherein theirrespective buoyant densities correspond to that of the solution.

During centrifugation of bowl-type rotors tremendous hydrostaticpressures are developed within the rotor at the extremities or outerwalls of the bowl. The hydrostatic pressures tend to force the wall ofthe rotor outwardly and also create an upward thrust on the cover in theregion adjacent the joint between the bowl rotor and its cover. Theoutward pressure on the rotor walls also creates a moment of forcearound the rotor bowl which, in turn, creates an upward thrust at thecentral portion of the bowl. The hydrostatic forces are so great thatthey sometimes cause separation between the cover of the bowl and thewall of the rotor where connected and result in a leakage of the liquidsolution from the rotor. In an attempt to overcome this, a resilientseal, such as a resilient O-ring, is sometimes employed between therotor wall and 'the cover which will prevent leakage of the solutionfrom the rotor chamber. However, the seal member around the cover or thesidewall of the rotor is placed under extreme stress during the highspeed centrifugation and, when the rotor and lid separate, the force ofthe solution on the seal very often causes the seal member to extrude.from its seat thereby releasing the solution from the chamber.

SUMMARY OF THE INVENTION In accordance with the invention, there isprovided an improved bowl-type zonal centrifuge rotor including a basehaving a substantially cylindrical sidewall forming a bowl-shapedchamber over which is mounted a cover member and which is attached tothe cylindrical sidewall. A resilient flexible sealing lip protrudesinwardly from the sidewall over the rotor chamber, the lip having asmooth surface adapted to abut against the coverin the region of aresilient sealing member or O- ring seated in an annular slot formed inthe cover. The flexiblelip maintains a sealing pressure against thecover and its O-ring and, under hydrostatic pressure created duringcentrifugation, the flexible lip moves with any slight movement of thecover to maintain a constant sealing pressure against the O-ring. Acentral core positioned within the rotor between the cover and thebottom of the chamber provides a vertical thrust against the bottom wallof the rotor chamber which thrust is opposite from the moment of forcecreated by the centrifugal forces on the sidewall of the rotor. Thisreduces the upward displacement of the bottom wall of the rotor andreduces the movement of the sidewall in a direction radial to the axisof rotation.

It is an object of the present invention to provide a new and improvedbowl-type rotor with an attached cover in which the hydrostatic forces,created by the liquid within the rotor during centrifugation, arereduced in the region of the seal between the cover and the sidewall towhich it is attached.

It is another object of this invention to reduce the deflection betweenthe cover and the sidewalls of the bowl by reducing the hydraulic axialloading on the cover. 7

It is another object of the present invention to provide a bowl-typerotor having a central core designed to oppose the upward thrustnormally occurring in the bottom central portion of the bowl-shapedrotor during high speed centrifugation.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention will be pointed out: with particularity inthe claims annexed to and forming a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofa rotor bowl assembly made in accordance with the present invention;

FIG. 2 is a plan view taken generally along the line 22 with portions ofthe rotor bowl assembly broken away to illustrate the location of thecentral core and the core wings with respect to the chamber in therotor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,and, more particularly, to FIG. I, there is shown arotor bowl 1 having asubstantially cylindrical sidewall 4 enclosing a bowlshaped chamber 3over which there is positioned a lid or cover member 2. In order toretain the cover 2 in place, the sidewall 4 of the rotor is providedwith threads 5 adjacent the open end thereof and the outer edge portion4a of the rotor sidewall is adapted to fit snugly within an annularcavity 6 formed in the cover 2. Threads 7 on the cavity wall are adaptedto mate with the thread 5 on the rotor sidewall so that the cover may bethreaded down tightly onto the sidewall of the motor. The overhangingedge 2a of the cover helps retain the sidewall 4 in place against thecentrifugal forces produced during high speed rotation of the apparatus.In the base portion la of the rotor, there is provided a well 8 which isadapted to receive a drive spindle (not shown) extending from thedriving mechanism of a centrifuge apparatus.

Within the chamber 3, there is provided a rotor core or centerpiece9which is a relatively solid member, formed of a suitable metal, andwhich is tapered slightly in an outward direction from bottom to top.The core is provided with a plurality of slots 12 (see FIG. 2) formed inthe outer surface thereof in a direction parallel to the vertical axisof the core 9. A plurality of pro jecting vanes or wings 11 (three ofwhich are shown in FIG. 2) each have one end positioned in one of theslots 12 and extend radially outward thereby dividing the rotor chamberinto equal sector compartments for minimizing turbulenceduring operationof the apparatus. Because the core or centerpiece 9 is subjected to highaxial loading and because the core wings 11 must extend to the cavitywall under the lip 47, it is necessary to construct the core 9 and vanes11 as separate parts and assemble them in the rotor chamber 3.

In assembling the rotor core 9 within the chamber 3, the vanes 11 arefirst inserted into the camber 3 and positioned generally into theirrelative positions therein. The core 9 is then inserted into the chamberso that the ends of the vanes extend into slots 12 formed in the rotorcore. In order to facilitate insertion of the core or centerpiece 9 andpermit orientation of the vanes 11 within the slots 12, each of theslots 12 is indented in the lower end adjacent the bottom of the coreand tapered or beveled to form a ramp so that there is a slighttolerance, permitting the ends of the vanes to fit initially into theslots 12. As the core centerpiece 9 is moved downwardly into thechamber, the ramp 10 forces the vanes 11 outwardly against the innersurface of the sidewall of the motor chamber. The outer ends of thevanes 11 conform to the bowl shape of the chamber and fit snugly againstthe sidewall beneath the lip 47. The rotor core abuts the bottom 32 ofthe cavity and legs or abutments 31 support the core thereon.

Inserted centrally within the rotor core is a feed or transfer tubeassembly 13 which extends downwardly through an aperture 14 formed inthe cover 2 into a cavity 16 formed in the rotor core 9. The lower endof the transfer tube 13 is provided with screw threads 17 which matewith internally formed threads 18 formed within the cavity 16 of therotor core. The transfer tube 13 includes an outer conduit 19 (orplurality of conduits 19) formed as slots in the outer surface of theshaft 13. Slots 19 communicate with an enlarged opening 16a in the upperportion of the rotor core. This opening 160 in turn communicates withradial passages 22 in the wall of the core each of which communicatewith passages 23 extending through each of the vanes or Wings 11 andopening into the chamber 3 at the end of each wing. An opening 24,formed in a beveled or cutaway portion 26 of each vane, communicateswith the upper portion of the chamber. The core member acts as amanifold to deliver fluids into each of the vanes 11.

The feed or transfer tube 13 is also provided with a central tubularconduit 27 which extends completely through the axial length of thetransfer tube and communicates with apassage 28 formed in the lower endof the core. Passages 29 formed in the lower end of the rotor core 9 bymeans of abutments or shoulders 31 communicate with the passage 28 inthe core. At least one of the passages 29 leads into each of thesegments between the vanes 11 within the chamber. Attached to the upperend of the transfer tube is a cup 34 having an opening 35 therein whichcommunicates with the passages 19 and 27 in the transfer tube. Inoperation, a liquid delivery means (not shown) is inserted into theopening of the cup 34 for introducing liquid gradient and samplematerials through the passages 19 and 27 and thence into the rotorchamber. Cup 34 is firmly attached to the end of the transfer tube 13and is tightly pulled downwardly against the upper surface 36 of the lid2 so that an O-ring 37 formed within an annular slot in the lowersurface of the cup abuts in sealing fashion against the upper surface 36of the lid.

In order to provide a seal between the passages 23 formed in the vanes11 and the passages 22 formed in the rotor centerpiece, a small O-ringor resilient seal ring 41 is provided within an enlarged openingsurrounding the pasage 23. O-ring 41 seals around the surface of thepasage 23 and the surface of the core leading into the opening 22.Another resilient seal member 42 is fitted within a slot formed on thesurface of the transfer tube 13 and abuts against the inner surface ofthe cavity 21 in the upper end 16a of the core centerpiece. This seal 42prevents the flow of liquid beyond the upper end 16a of the cavity 21and forces liquid from the cavity into the passages 22 and thence intothe passages 23 formed in vanes 11. In order to prevent leakage aroundthe upper surface of the core centerpiece 9, there is also provided anannular sealing means in the form of a resilient O-ring 43 positionedwithin an annular slot 44 in the upper surface of the core. The O- ring43 abuts against the lower surface 46 of the cover 2 when the cover istightened down onto the rotor. In addition the cover actually has itslower surface 46 abutting tightly against the upper flat surfaces of thecore.

In a typical operation of the above-described rotor,

a rotatable liquid delivery means (not shown) is inserted into the cup34 through which a liquid may be pumped into the rotor. The rotor bowlis first loaded with a liquid gradient which is pumped into the bowlthrough the conduits 19, 21, 22 and 23. During the loading operation,the rotor bowl is rotated at a low speed (5003,000 r.p.m.) causing thegradient liquid to form concentric annular zones of constant densityliquid. The vanes 11 extend radially through the zones," segmenting themand reducing mixing between adjacent zones of different densities. Afterthe rotor bowl is filled with a liquid of graded density, a sample to becentrifuged is pumped through the conduit or transfer tube passage 27where it flows through the passage 28 and the passages 29 beneath therotor core into the center portion of the rotor chamber. The sample isnormally followed by an overlay of low density liquid to move the sampleclear of the core 9 and to assure complete removal of the sample frombeneath the rotor core. The means for inserting the liquid materialsinto the rotor is then removed and the cap 34 is closed with a suitablesealing cap (not shown) to close the passages 19 and 27. The rotor isthen accelerated for the actual centrifuging operation.

When centifugation has been completed, the rotor bowl is decelerated tounloading speed (SOD-3,000 r.p.m.) and the rotor contents emptiedthrough the liquid delivery means by pumping high density fluid to theouter wall of the rotor cavity through the passages 19, 21 22 andpassages 23. The high density fluid forces the gradient and the sample,dispersed in the annular gradient rings, toward the rotor core 9 and thetaper on the exteral surface of the rotor core forces each of thegradient rings to flow downwardly through the passages 29 and up thecentral passage 27 of the transfer tube and thence out through thedelivery means attached to the upper end of the transfer tube.

As the rotor is subjected to the high angular velocity by a drive hub at8, the resulting hydraulic forces within the chamber cause the cover 2and the bowl 1 to tend to move relative to one another. These membersare restrained only by the threads and the overhanging lip 2a of thecover at 2a. This hydraulic force is proportional to the fourth power ofthe maximum radius at which it can act, In order to effectively reducethe radius at which these forces may act on the cover, the rotor isprovided with a lip 47 extending from an upper portion of the sidewall4,, which intrudes radiallyinto the clearance volume adjacent the lid 2of the rotor. The lip 47 has a lower curved surface 470 and an upperflat surface 471). At its base or connection with sidewall 4, the lip isrelatively thick but it gradually tapers toward the end intruding intothe chamber.

The thinner portion of the lip 47 are somewhat resilient and flex underthe influence of axial hydraulic force such that as the lid 2 movesupwardly under the hydraulic pressure, the lip 47 moves just enough tofollow the covers motion and maintains contact with a resilient O-ringseal 48 positioned in an annular slot 49 within the lower surface of thecover. The upper surface 47b of the lip 47 is flat and maintainscontinuous contact with the O-ring 48 as the cover and sidewalls of themotor move relative to each other. At the base of the lip 47, it is muchthicker and much less resilient so that any load exerted by thehydraulic forces is prevented from being transmitted to the cover inthis region. The hydraulic forces may be transmitted in an upwarddirection toward the cover only at the inner, edge of the resilient lip47. Since this is at a radius much less than the outer extremity of therotor wall, the hydraulic pressure exerted against the inner surface ofthe cover 2 is less than would normally be present if there were noresilient lip or seal abutting the lower surface of the cover.

Under the influence of centrifugal force, the wall of the rotor at 51tends to move radially outward. Since this wall is attached to the baseand restrained by the base, this tendency to move outward results in amoment about the center of the base causing the center to move upwardlyrelative to the threads of the cylindrical wall at 7. This upwardmovement of the central portion of the base is restrained by virtue ofthe force exerted by the cover 2 downwardly against the heavy metalliccore member 9 which tends to exert a force axially against the base. Byrestraining the center of the base from bulging upward by the use of therigid central core 9, the radial excursion of the sidewall 4 of therotor is reduced with a corresponding reduction in stresses in thesidewall 4 under high speed centrifugation.

While in accordance with the patent statutes there has been describedwhat at present is considered to be the preferred embodiment of theinvention, it will be understood by those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the invention, and it is, therefore, the aim of the appended claimsto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A rotor for a centrifuge apparatus comprising a rotatable bowl havinga base and a substantially cylindrical sidewall forming a chamber havingan open side substantially coextensive with'said cylindrical sidewall;

a cover for closing said open side of said chamber;

means for securing said cover to said sidewall of said rotatable bowl;and t a resilient lip attached to said-sidewall and overhanging saidchamber, said lip having an upper surface engaging the lower surface ofsaid cover, said lip having sufficient resiliency to permit it to moveand follow movement of said cover thereby maintaining sealing contactwith said cover during centrifugation of liquid products withinsaidchamber.

2. A rotor for a centrifuge apparatus comprising a rotatable bowl havinga base and a substantially cylindrical sidewall forming a chamber havingan open side substantially coextensive with said cylin-.

drical sidewall;

a cover for closing said open side of said chamber,

including means engaging said sidewall for supporting said cover oversaid chamber, said cover having a substantially flat lower surface;

means for delivering liquid gradient and sample products through saidcover into said chamber; and

a resilient lip attached to said sidewall and overhanging said chamber,said lip having an upper surface engaging said substantially flatsurface of said cover, said lip having sufficient resiliency to permitit to move and follow movement of said cover thereby maintaining sealingcontact with said cover during centrifugation of liquid products withinsaid chamber.

3. The rotor defined in claim 2 in which said cover includes an annulargroove formed. in the lower surface thereof in which is mounted aresilient O-ring and said resilient lip extending from said sidewall isso constructed and arranged as to engage said O-ring and follow movementthereof to maintain sealing contact with said O-ring duringcentrifugation of liquid products within said chamber.

4. The rotor defined in claim 1 in which said resilient lip isrelatively thick at its attachment to said sidewall and graduallyreduces in thickness to form a resilient portion which moves in responseto hydrostatic pressure in said chamber created during centrifugationthereby forcing said resilient lip to maintain contact with said cover.

5. The rotor defined in claim 4 in which said cover is provided with anannular groove in the lower surface facing said chamber, and an O-ringis disposed in said groove and said resilient lip is so positioned anddisposed as to engage said O-ring thereby maintaining sealing contactwith said O-ring and said cover during centrifugation of liquid productswithin said chamber.

1. A rotor for a centrifuge apparatus comprising a rotatable bowl havinga base and a substantially cylindrical sidewall forming a chamber havingan open side substantially coextensive with said cylindrical sidewall; acover for closing said open side of said chamber; means for securingsaid cover to said sidewall of said rotatable bowl; and a resilient lipattached to said sidewall and overhanging said chamber, said lip havingan upper surface engaging the lower surface of said cover, said liphaving sufficient resiliency to permit it to move and follow movement ofsaid cover thereby maintaining sealing contact with said cover duringcentrifugation of liquid products within said chamber.
 2. A rotor for acentrifuge apparatus comprising a rotatable bowl having a base and asubstantially cylindrical sidewall forming a chamber having an open sidesubstantially coextensive with said cylindrical sidewall; a cover forclosing said open side of said chamber, including means engaging saidsidewall for supporting said cover over said chamber, said cover havinga substantially flat lower surface; means for delivering liquid gradientand sample products through said cover into said chamber; and aresilient lip attached to said sidewall and overhanging said chamber,said lip having an upper surface engaging said substantially flatsurface of said cover, said lip having sufficient resiliency to permitit to move and follow movement of said cover thereby maintaining sealingcontact with said cover during centrifugation of liquid products withinsaid chamber.
 3. The rotor defined in claim 2 in which said coverincludes an annular groove formed in the lower surface thereof in whichis mounted a resilient O-ring and said resilient lip extending from saidsidewall is so constructed and arranged as to engage said O-ring andfollow movement thereof to maintain sealing contact with said O-ringduring centrifugation of liquid products within said chamber.
 4. Therotor defined in claim 1 in which said resilient lip is relatively thickat its attachment to said sidewall and gradually reduces in thickness toform a resilient portion which moves in responsE to hydrostatic pressurein said chamber created during centrifugation thereby forcing saidresilient lip to maintain contact with said cover.
 5. The rotor definedin claim 4 in which said cover is provided with an annular groove in thelower surface facing said chamber, and an O-ring is disposed in saidgroove and said resilient lip is so positioned and disposed as to engagesaid O-ring thereby maintaining sealing contact with said O-ring andsaid cover during centrifugation of liquid products within said chamber.